1. Field of the Invention
The present invention relates a white balance correction of an image captured by an imaging apparatus.
2. Description of the Related Art
Imaging apparatuses using an image sensor such as a digital camera and a digital video camera are provided with the white balance control function for adjusting a color tone of an image captured by an imaging operation. This white balance control includes manual white balance control and automatic white balance control. The manual white balance control calculates a white balance coefficient by capturing a white object in advance and applies the calculated white balance coefficient to the entire screen. The automatic white balance control automatically detects a possible white portion from a captured image, calculates a white balance coefficient from an average value of each color component in the entire screen, and applies the calculated white balance coefficient to the entire screen.
Even when there is a light source different from a flash light in a scene that an imaging apparatus captures an image while emitting the flash light, the conventional automatic white balance control applies the white balance coefficient calculated as mentioned above to the entire screen. Therefore, it is difficult to perform the white balance control so as to achieve appropriate color tints for both the light sources. For example, in a scene that an imaging apparatus emits flash light which is a light source having a high color temperature, if the ambient light contains a low color temperature light source such as an electric light bulb color source, controlling the white balance based on the flash light results in unsuitable white balance for the low color temperature light source in the ambient light. On the other hand, controlling the white balance based on the low color temperature light source in the ambient light results in unsuitable white balance for the flash light. Further, even if the imaging apparatus performs the white balance control by adjusting the white balance to the middle between the respective light sources, this results in unsuitable white balance for both of the light sources, leading to generation of an image in which a region irradiated with the flash light in tinged with blue while a region irradiated with the low color temperature light source is tinged with red.
To solve this problem, the technique discussed in Japanese Patent No. 3540485 discloses as follows. This technique calculates a data ratio by comparing an image data captured while the flash light is emitted to an image data captured while the flash light is not emitted for each arbitrary object region, and determines a degree of contribution of the flash light based on the calculated ratio value, and determines a degree of contribution of the flash light based on the calculated ratio value. This technique performs the white balance control by selecting a white balance control value for each region for video data captured in an exposure with the flash light, according to the degree of contribution.
The technique discussed in Japanese Patent No. 4389671 discloses as follows. This technique extracts flash light components from an image captured while the flash light is emitted and an image captured while the flash light is not emitted. This technique detects areas in which an object blurs when an white balance control is switched in accordance with each of the flash light components, calculates a white balance coefficient for areas in which object does not blur and a white balance coefficient for the areas in which the object blurs using interpolating, and applies the calculated coefficients to the image data. To detect the areas in which the object blurs, high frequency components of the image data are detected.
The conventional technique discussed in Japanese Patent No. 3540485 has to estimate the irradiation amount of the flash light by calculating a difference between the image data captured while the flash light is emitted and the image data captured while the flash light is not emitted, and to perform the white balance control in accordance with the estimated irradiation amount. However, when the object is moving, it is impossible to estimate the irradiation amount and to perform the white balance control correctly. As a result, spots pattern is generated on the image data and high quality image is not be able to obtained.
The conventional technique discussed in Japanese Patent No. 4389671 adopts a method which detects the areas in which the object blurs by detecting the high frequency components. However, it is impossible to discriminate between the high frequency components which the image data has originally and the high frequency components caused by the object blurring and hands blurring. As a result, optimum white balance control is not be able to performed and high quality image is not be able to obtained.